I tried a set of Aftermarket cats on my 300TE once. I will never do it again. They cause too much back pressure, killed 2 o2 sensors, and continually triggered my check engine light...

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-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.